The present invention relates generally to lead assemblies for medical devices, and more specifically to a method and apparatus for providing a secure electrical connection between wound elements, as found in unifilar and multifilar coil conductors, and electric elements, such as lead connector pins, electrodes, sensors and various other elements employed in lead assemblies for implantable medical devices.
Implantable leads form an electrical connection between a pulse generator or other electronic device and a tissue or structure in the body. For example, leads transmit electric signals used to stimulate cardiac or nerve tissue in one direction and signals generated by sensors placed in proximity to particular organs or tissues in the opposite direction. Leads typically include one or more electric elements at the lead""s distal end. The electric elements are designed to form an electrical connection with a tissue or organ. Most leads also include a lead connector pin at the lead""s proximal end. Lead connector pins are adapted to electrically and mechanically connect leads to the pulse generators or other electronic medical devices. A flexible conductor connects the electric element to the lead connector pin. Commonly, the flexible conductor takes the form of a single or multifilar wire coil. Although, there is an increasing interest in using stranded cables as conductors. Regardless of the form, the flexible conductors are typically surrounded by an insulating layer of material. Together, the flexible conductor and the insulating layer form the lead body. The lead body couples the lead connector pin at the proximal end with the electric element at the distal end.
Manufacturing leads is costly. Forming a secure electrical junction between the conductors and electric elements has proven difficult and time consuming. Laser welds are commonly used to connect the filars or wires that make up the conductors to electric elements. The conductor""s filars are typically helically wound into a coil for increased reliability. Laser welding the coiled filars to electric elements typically requires that the end of a coil be ground flat. Grinding the ends flat allows sufficient contact between the coil and the electrical element to weld the two together with a butt joint. Grinding increases the time, complexity and cost of manufacture. Further, welding requires the synchronized rotation of the conductor and electric element to weld at the various points around their circumference. The rotating also adds to the time, complexity and costs of manufacture. Alternatively, ring electrodes are connected to a conductor by etching away a region of insulator, applying a coating of electrically conductive adhesive, and then placing the ring electrode around the conductor. This method is also time consuming and expensive. Hence, there exists a need to improve the manufacturing techniques used to secure electric elements to conductors in leads to reduce the time, complexity and cost.
In addition, current manufacturing techniques do not allow welding an electrical element to a coil without adding elements that increase the lead""s diameter near the weld. In application, a uniform diameter weld would result in a smaller lead. A smaller diameter lead is desired to allow placement in restricted spaces such as cardiac veins or the epidural space to reduce the effects of implanted lead on the patient. Further, a smaller lead allows for a smaller introducer that reduces the trauma associated with implantation and similarly a smaller removal sheath when explanting the lead. Hence, there exists a need to reduce the diameter of the welds used to secure electric elements to conductors in implantable medical leads.
The present invention meets these needs and provides other advantages and improvements that will be evident to those skilled in the art.
The present invention provides a uniform diameter junction for an implantable lead and reduces the time, complexity and costs of producing implantable electrical leads by allowing the use of a straight line weld of the conductors to the electric elements. In addition, the junction typically results in a uniform diameter connection between the lead body and the electric element.
In accordance with the present invention, a method and lead design are provided for longitudinally securing the cut ends of a conductor to an electric element. The present invention""s method for manufacturing an implantable medical device leads includes a conductor having at least one filar and an electric element having a longitudinal edge. The electric element can be a ring electrode, a terminal pin, a splice ring, a terminal ring, a lead connector pin, a sensor or other implantable medical device commonly attached to leads. The filars can be spirally wound into the conductor at a substantially constant pitch. The filars are cut in a direction parallel to a longitudinal axis of the conductor to form at least one collinear cut end. The collinear cut end is parallel to the longitudinal axis of the conductor. The ends are secured to the longitudinal edge of the electric element to provide an electrical connection. The cut ends can be secured to the electrical element by laser welding, resistance welding, soldering, swaging, electrically conductive adhesives, micro arc welding or by other methods known to those skilled in the art. In addition, the longitudinal edge can combine with a second edge to define a notch. The second edge is configured to have a pitch corresponding to the pitch of the filars. The corresponding pitch allows one of the plurality of filars to abut the second edge over the distance that the electric element and the conductor are coextensive. Further, the plurality of filars can embedded in an elongated, flexible elastomeric insulator. The insulator can define a lumen adapted to receive a stylet for guiding the lead into the patient. A portion of the insulator may be removed from the conductor""s proximate end prior to welding. Typically, the insulator is removed mechanically or by chemical etching.
The present invention further discloses an implantable lead for a medical device. The implantable lead includes at least one conductor and one or more electric elements. The conductor has one or more filars wherein each filars terminate in an end. The ends are typically generated by cutting using any of a number of techniques known to those skilled in the art. The ends are cut so as to be collinearly oriented in a direction parallel to a long axis of the conductor. The filars can be spirally wound into the conductor at a substantially constant pitch. The electrical element also has a longitudinal edge. The longitudinal edge is configured to contact the cut ends and the cut ends are secured to the longitudinal edge, typically in a laser-welding step. When the filars are wound at a substantially constant pitch, the electrical element can have a second edge having a pitch corresponding to the pitch of the filars. The longitudinal edge and a second edge of the electric element cooperate to define a notch extending inwardly from one end of the electric element. The notch is shaped so that one of the plurality of filars abuts the second edge over the distance that the electric element and the conductor are coextensive.